To prevent air leakage and maintain the air pressure of a tire constant, an inner liner made of a less air-permeability rubber such as butyl rubber and a halogenated butyl rubber is generally provided on the inner wall of a pneumatic tire. However, since the strength of a non-vulcanized rubber is reduced with increasing content of butyl rubber, a non-vulcanized rubber sheet is susceptible to rapture and hole defect. Particularly, when an inner liner is of smaller gauge, a cord provided inside of the tire easily comes out of the inner liner during the tire construction.
An airplane tire is sometimes exposed to an atmosphere as low as −65° C. Also, a heavy weight vehicle such as truck and bus is occasionally parked in extremely cold region, thereby exposing its tire to a low temperature as low as −50° C. Therefore, if the inner liner of a tire of a heavy weight vehicle is composed mainly of butyl rubber or a halogenated butyl rubber, each having a high glass transition temperature, cracking is liable to occur in the inner liner.
To meet the recent social demand for saving energy, various methods have been proposed in reducing the gauge of inner liner to reduce the weight of a tire. For example, Japanese Patent Application Laid-Open Nos. 7-40702 and 7-81306 propose to use a nylon film layer or a poly(vinylidene chloride) layer in place of butyl rubber. Japanese Patent Application Laid-Open No. 10-26407 proposes to use a film of a composition comprising a thermoplastic resin such as polyamide resins and polyester resins blended with an elastomer.
The proposed methods using the above films are, in some degree, successful in reducing the weight of tire. However, since the matrix of each film is a crystalline resin, the crack resistance and the flexural fatigue resistance are poor, particularly, when used at temperatures lower than 5° C., as compared with a layer generally used, which is made of a composition compounded with butyl rubber. In addition, the use of a matrix crystalline resin makes the process for producing a tire complicated.
Also known are a method of compounding flat mica as a filler for a rubber composition (Japanese Patent Application Laid-Open No. 11-140234) and a method of compounding a clay (Japanese Patent Application Laid-Open No. 5-017641). In these methods, however, the filler is not uniformly dispersed during a rubber kneading when the filling amount is increased, thereby likely to reduce the flexural fatigue resistance and the low-temperature durability because of insufficient dispersion.